The present invention relates to a radio receiver and to an intermediate frequency selection method. For example, the present invention relates to a radio receiver having a quadrature demodulator for generating an intermediate frequency signal, and to an intermediate frequency selection method used in such a radio receiver.
A receiver for receiving signals based on two communication methods, namely, the Bluetooth (registered trademark) communication method and the ZigBee (registered trademark) communication method, is disclosed in A 0.6-V Zero-IF/Low-IF Receiver With Integrated Fractional-N Synthesizer For 2.4-GHz ISM-Band Applications, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 45, NO. 3, Mar. 2010. This receiver includes a quadrature demodulator so that the quadrature demodulator converts a communication signal to an intermediate frequency (IF) signal. This receiver operates in a Low-IF (low intermediate frequency) mode when the Bluetooth communication method is used, and operates in a Zero-IF (zero intermediate frequency) mode when the ZigBee communication method is used. More specifically, the communication signal is converted to an intermediate frequency signal having an intermediate frequency of 2 MHz when a Bluetooth communication system is used, and is converted to an intermediate frequency signal having an intermediate frequency of 0 Hz when a ZigBee communication system is used. A 0.6-V Zero-IF/Low-IF Receiver With Integrated Fractional-N Synthesizer for 2.4-GHz ISM-Band Applications, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 45, NO. 3, Mar. 2010 also states that an analog filter disposed at the input stage of the quadrature demodulator is operated as a band-pass filter when the Bluetooth communication method is used, and that the analog filter is operated as a low-pass filter when the ZigBee communication method is used.
A receiver for receiving communication signals based on two communication methods is also disclosed in Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2004-515104. This receiver receives communication signals based on two communication methods, namely, the UMTS (Universal Mobile Telecommunications System) communication method and the GSM (Global System for Mobile communication) (registered trademark) communication method. This receiver operates in the Zero-IF mode when the UMTS communication method is used, and operates in the Low-IF mode when the GSM communication method is used.